In various wireless communication systems, such as WiMAX (Worldwide Interoperability for Microwave Access), next generation PHS (Personal Handy-Phone System), and LTE (Long Term Evolution), MIMO (Multiple Input Multiple Output) is used which is a communication technique through use of a plurality of antennas on both sides of a transmitting side and a receiving side aiming at improving throughput and frequency use efficiency.
The MIMO communication scheme includes an STC (Space-Time Coding) scheme and an SM (Spatial Multiplex) scheme (e.g., see Patent Document 1 (Japanese Patent Laying-Open No. 2009-273186)).
Under the STC scheme, a communication apparatus arranges (i.e., codes) one signal stream based on a certain rule in terms of time and space (antenna), and transmits a coded signal stream through a plurality of antennas. On the other hand, under the SM scheme, a communication apparatus multiplexes a plurality of signal streams at the same frequency through a plurality of antennas.
Switches are made in MCS (Modulation and Coding Scheme) and the MIMO scheme depending on wireless performance, such as error rate. Since communication by the SM scheme is likely to become unstable, a switch to the SM scheme is generally made with a margin.
That is, generally, a communication apparatus utilizes the STC scheme in the initial state, and increases the level of MCS as wireless performance becomes better. If the wireless performance becomes still better after arriving at MCS at which the maximum throughput can be obtained by the STC scheme, a switch is made to the SM scheme.